The Harmour (known as EvilArmor in this game) can be obtained by breeding a Devil family monster with an Armorpede. The easiest way to do this is to obtain a Demoneye or 1EyeClown, and wait until you complete the pirate world. There will be a man, that looks similar to the King in the Oasis world, waiting by the entrance to the Monster Arena, with an Armorpede. Accept his offer to breed a monster with him to obtain the EvilArmor egg, which you can then evaluate or bless.

EvilArmors also appear as minibosses inside Mudou (Murdaw)'s Castle as guards. They always appear in pairs.

The man also hints to you: "If you get an EvilArmor, you should breed it with a material type monster. Isn't that a tough combo?"